Air swept pulverizer for use in closed-circuit pulverized material transport systems



Feb. 24, 1948. R, HARDGROVE 2,436,488

AIR SWEPT PULVERIZER FOR USE IN CLOSED-CIRCUIT PULVERIZED MATERIAL TRANSPORT SYSTEMS Filed D80. 11, 1945 2 Sheets-Sheet 1 uvv'szvron.

Ralph M Hare/grove BY A TTORNE Y Feb. 24, 1948. R. M. HARDGROVE 3 8 AIR SWEPT PULVERIZER FOR USE IN CLOSED-CIRCUIT PULVERIZED MATERIAL TRANSPORT SYSTEMS Filed Dec. 11, 1943 .2 Sheets-Sheet 2 INVENTOR. Ea/ph MHardgml e BY A TTORNE Y Patented Feb. 24, 1948 UNITED STATES PATENT OFFICE AIR SWEPT PULVERIZER FOR. USE IN CLOSED-CIRCUIT PULVERIZED MA- TERIAL TRANSPORT SYSTEMS Ralph M. Hardgrove, Westfleld, N. J assignor to The Babcock & Wilcox Company, Rockleigh, N. J a corporation of New Jersey Application December 11, 1943, Serial No. 513,841

Claims.

The invention herein disclosed relates to a pulverizing apparatus especially adapted for use in a system wherein pulverized products are trans-' ported from the apparatus by means oi! a current of air or other suitable gaseous carrier medium, and varying proportions of such products are returned to the apparatus for recycling. The apparatus and system will be found suitable for use with materials of various composition including, for example, such solids as coal, mineral ores, cement clinker, or other solids of similar physical characteristics.

The invention may be usefully applied in a pulverized fuel firing system wherein pulverized.

coal is discharged from the pulverizer in a stream of carrier air, and the resulting fluent mixture delivered to a burner, or to a number of burn ers, with any surplus quantity oi the mixture being returned to the pulverizer to provide continuous circulation. .In such a system, provision is made for feeding raw coal to the pulverizer at rates suflicient to replace the amounts taken by the burner or burners. and for supplying fresh or make-up air to the pulverizer at rates sumcient to maintain a current of air therethrough at all loads while providing an output mixture having the particular iuel-to-air ratio desired for any given load.

In certain types of pulverizers wherein grinding elements are relatively rotatable about a vertical axis, the coal and make-up air are conveniently supplied to the pulverizing zone from opposite sides, that is, the raw coal being fed from the upper side for discharge by gravity into the zone, and the fresh air being supplied from the under side for admission to the zone in an' and air are supplied to the pulverizer in such 1 proportions that the. resulting output mixture contains a smaller quantity of air than is necessary for complete combustion: thus, the mixture with its normal content of primaryair may be transported from the pulverizer without, risk of premature combustion or explosion, and the required amount of secondary air may be added at the burners to provide a suitably combustible mixture.

When a surplus of the mixture is returned to the pulverizer, as in the circulating system herein disclosed, the fuel and air content of the returning mixture remains essentially the same as when originally discharged from the pulverizer, a relatively high velocity of flow being maintained'throughout the return conduit system to prevent any appreciable quantity of pulverized coal from settling out of the returning stream. When the return mixture and the make-up or primary air are combined for flow through the grinding zone, the proportion of air in the resulting mixture is appreciably higher than in the returning fuel air mixture, thereby tending to provide an atmosphere capable of supportingcombustion of the entrained coal particles. It is considered important therefore to avoid any condition which might lead to, ignition or such 'a mixture to cause a possible explosion, either lations in or adjacent the zone of mixing, or as a result of hot" coke particles being carried into the mixing zone and allowed to accumulate therein. When a heated supply or primary air is em ployed, the hazard of the mixture becoming ignited is somewhat increased, due to a certain amount of heat being retained in the returning coal-air mixture which would tend to promote coke formation.

It is a purp se of the invention therefore to maintain the fluid flow'passfl-sqs leadins t0 the grinding zone clear of all coal or coke accumulations, and to cause'the make-up air and the returning coal and air to be mixed in a zone where there is the least tendency for coal or coke to collect.

An additional object is to maintain fluid flow velocity cpnditions in and adjacent the mixing zone of a character maintaining the adjoining passages clear 01' any pulverized coal or coke that might tend to settle therein; in general. the velocities for the make-up air beingsubject to variation over a considerable range. while the velocities for the dust-laden stream are maintained more nearly constant.

Another object is to cause the respective r streams to enter the mixing zone in such direc tions and at such velocities as to promote thorough mingling of the streams throughout the, zone.

. A further object is to provide a mixing man having an outlet direct to the grinding zone or adjoining region where the issuing stream will ensues pick up additional coal particles which being nioist, reduce the temperatureabmptly, thereby increasing the proportion of coal to air in the mixture and providing a relatively non-explosive mixture for flow through and from the pulverizer, the area of now from the mixing zone into the grinding zone to be small enough to maintain flow velocities at leastas high as the velocities prevailing within the mixing zone, and higher than the rate of flame propagation for the fuel and air mixture in transit at that location.

Among other objects, it is proposed to main-' tain the passages leading to and from the mixing zone clear of oversize particles or other forsign materials which might tend to obstruct the flow of air and pulverized coal.

More specific objects include the admission .of coal-free air and coal-laden air to the'pulverizer through concentrically arranged inlet areas; the mixing of both bodies of air in an annular zone closely adiacent the grinding zone; and the admission of both bodies of air to the pulverizer in the same direction, with subsequent reversal of flow of one body of air for mixing in a surrounding annular zone. y

The foregoing objects and others not specifically mentioned are more fully set forth, in the description to follow, together with various advantageous features of construction asillustrated in the accompanying drawings, in which:

Fig. 1 is a layout, in plan, of a pulverized coal circulating system embodying apparatus of my invention;

Fig. 2 is a sectional assembly of the pulverizer included in the system of Fig. l;

Figs. 3 and! are plan sections of the pulverizer assembly shown in Fig. 2, taken along lines 3-3 7 and 4-4 respectively: and

Fig. 5 is an enlarged fragmentary outline of parts shown in Figs.2and 3.

air to any burner not in operation; and to regulate the supply of fuel to the various burners durof the. looped arrangement of the conduit 24 which provides a closed circulatory system. A secondary supply of air may be admitted to the burners or to the furnace or furnaces for complete combustion of the fuel, but the details of such secondary supply are not included in the present invention, and further disclosure is therefore considered unnecessary.

V The references to coal as the material being pulverized, and to air as the carrier medium, are not to be taken literally, but are to be interpreted as embracing other solids. combustible or otherwise, and othergaseous media, capable of adaptation to thesystem described. in a broad sense also, the burners i2 and I4 become selected points of delivery or use, for example, bins or other containers, irrespective of whether the material transported is a fuel or is a material of non-combustibl character.

Referring to Fig. 2, the pulverizer i0 is, by way of example, of a known bail-mill type having its grinding zone located in the lower portion of an enclosing casing or housing 34 generally circular in cross-section about a vertical axis. The grinding elements include a circular series of grinding The system according to Fig. '1 of the drawings includes an air swept pulverizer i0 arngnged to supply pulverized coal and primary air'to burners I2 and I4 associated with a form of metal lurgical furnace it, here indicated as abillet heating furnace, although as will be understood,

other types of furnaces may be employed and, if

desired, the burners arranged for firing separate furnaces. J

The pulverizer I0 is shown as being located adjacent the charging end ll of the furnace l6 and its output of pulverized coal and primary air is discharged through pipe to the inlet of an exhauster fan 22 from which the mixture is delivered to a main distributor conduit 24 at its inlet end 26, the opposite end or return length 28 of the conduit being connected to the air inlet side of the pulverizer to form a closed circuit or loop as will be explained more in detail hereinafter. The pulverizer and fan are conveniently operated by a single motor 30.

The loop conduit 24 is tapped at successive positions along its length to supply a mixture of ing or housing ii. A conical wall I2 surrounding the lower grinding ring 42 and flaring upwardly toward the casing 30 serves to guide the incoming raw coal into the zone of action of the balls N. The upper grinding ring 40, concentric with the lower grinding ring ,42, is rotated about its central vertical axis to cause the balls 38 to roll relative to both grinding rings; the upper grinding ring 4| being driven by motor 30 operating through pinion shaft 84, gearing within the housing 88, a spider member 58, and a drive ring pulverized coal and air to any one of the burners, or group of burners, that it may be desired to i0. Grinding pressure between the balls and rings is resiliently and adjustably maintained in the usual manner by means of circumferentially spaced springs l2 seated at their lower ends against the drive ring 80.

A bell shaped member 84, rotatable with the drive member 58 and constituting an integral extension thereof, terminates in a lower rim portion I! of bulbous cross-section at alevel correspondlng to the reduced inner edge portion 68 of the lower grinding ring 42, thereby forming a relatively narrow annular passage or throat ll through which carrier air is admitted to the grinding zone. The coal is fed to the region exteriorly of the circle of balls 38 and as the coal becomes pulverized, the particles are swept upwardly by the stream of carrier fluid admitted to the grinding zone through the throat Hi, the majority of the pulverized particles being carried upwardly in the region interiorly of the circle and discharged laterally through a circumferential positively cut oil the supply or fuel and primary (4 series of ports 12 in the drive ring In. The finer particles continue upwardly through the chamber 44 and are discharged from the pulverizer through the outlet 28, while the coarser particles drop out of the current and are returned to the pulverizing zone for further reduction. A plow I4 attached to the rotating grinding ring 48 serves to agitate the'mass of coal to be pulverized so that the coal may move freelyinto the zone of action of the balls 88.

The extension member. is provided exteriorly with a series of circumferentially spaced vanes I8 adjacent/its lower rim portion 88, such vanes being inclined to the vertical at an angle of about forty flve degrees, the direction, of inclination being determined by the direction of rotation of the member 84 which for the structure illustrated will be understood to be counterclockwise'asinr 6 tion of duct 84 and defines'the perimeter of the duct outlet which registers with the outer diameter of the annular area 98. The bottom wall portion I28 of duct 84, from approximately the center line position I22, is inclined to the horizontal at a considerably greater.v angle than the general line of flow through'the duct at preceding positions, the wall portion or bottom plate I28 being flat and extending upwardly to a position above the flange I I8 to provide an inclined projecting lip I24 subtending an angle of approximately 60 to 75 degrees measured horizontally about the central axis of the annular outlet dicated by the arrow"in--fig 3. Plow I8, dia

82 may be heated or unheated. as desired, and

the duct fitted with the usual regulating damper or dampers, a supply of heated air being suitably admitted through opening 82a under control of damper 88 and a supply of cooler tempering air being suitably admitted through a branch opening 82b under control of damper 85. The air inlet duct 82 is formed by-circular pipe sections 88 and 88 Joined in elbow relation to provide upward flow of air into the space 88 interiorly of the bell-shaped extension member 84; the section 88 extending vertically through the circular base plate opening 82 and terminating in an outlet 84 coaxial with the extension member 84 at an appreciable distance above the bottom rim portion 68'; thereby defining an annular space 88 between the section 88 and the wall of the opening 82; and an annular space 88 between the section 88 and the rim portion 68 of member A throat ring I88 integral with and surrounding the inlet pipe section 88 is formed with upper and lower conical deflecting surfaces I82 and I84 positioned below the throat passage I8, the purpose of such surfaces to be later defined. A stationary guide plate I88 extends from the perimeter of the base plate opening 82 to the top edge of the annular support 48 thereby providing an upwardly flaring conical surface I 88 for directing the flow of air and fuel toward the throat passage 18.

The return duct 84 for the surplus pulverized coal and air mixture forms a continuation of the major portion of its length and, being inclined upwardly from its connection with the return pipe length 28, is fitted with a plug insert door II8 for inspection and cleaning. A transition is made in the horizontal width dimension of the area 96, and having its peripheral edge circular as seen in horizontal projection.

In thezoperation of the system described, the air admitted-to the pulverizer through duct is discharged axiallytand upwardly into the space 88 interiorly of the spiderextensidh 84. The direction of air flow is then reversed and the ,air caused to flow downwardly through the annular passage 88 formed between the inlet pipe section 88 and the rim 86 at the lower open end of the rotating member 84. The make-up air thus approaches the throat ring I88 from above and is deflected outwardly by the concave conical upper surface I82 of the ring toward the upwardly flaring surface I88 of the surrounding conical plate I88. The mixture of fuel and air returnin from conduit 24 through duct 84 is admitted to the pulverizer through the annular opening 86 and thus approaches the throat ring I88 from below, the fluent mixture being deflected outwardly by the conical under surface I84-of the ring also toward the upward flaring surface I88 as in the case of the entering make-up air. As a result, the'two streams are combined and thoroughly ,mingled to provide a single stream of substan tially uniform density for flow into the "pulverizing zone through the throat 18, the streams being mingled in a region immediately adjoining the duct 84 as it approaches the annular outlet space 88, the transition from the normal width dimension at location II2, for example, including diverging side wall portions II4 together with continuing curved wall portions H8 terminating ad- Jacent the perimeter of the base plate opening 82. An annular flange III forms a top wall por- 78 throat where the velocities are maintained sufficiently high .to prevent solids dropping out of suspension, thus obviating a possible interference with free circulation of the returning fuel by particles accumulating in the various ducts and passages. The circulation Of fluid through the pulverizer isalso assisted by the vanes I6 and plows I8 which 'keep the solids constantly in motion to prevent obstruction of the narrow annular passages I8 and 88 respectively.

I claim: a

1. In a pulverizer having grinding elements in the lower portion of an enclosing housing, said housing having an outlet leading from its upper portion, said elements including a member formed with a grinding surface arranged annularly about -a vertical axis between a material inlet circumference and a material outlet circumference disposed at different radial spacings from said axis, means for feeding material to be pulverized to a region adjacent said inlet circumference, means forming an annular throat adjacent said outlet circumference. means for causing air to flow through said throat for transporting particles of pulverized material to and through said outlet, means for admitting said air to said pulverizer in separate upwardly directed concentric streams of which an inner stream is composed of relatively clean air and an outer stream is composed of air in which pulverized material particles are suspended, said inner air stream being admitted to the interior of said housing at a level higher than the level of admission of said outer particlesuspending stream, means defining an annular aasaasa space in the region below and adjacent said throat, means for causing said streams to become mingled in said. annular space to form a substantially homogeneous iluent mixture, and means for directing said mixture upwardly through said throat.

2. In an air swept pulverizer adapted for inclusion in a pulverized material circulating system wherein a fluent mixture of material and air is continuously discharged from said pulverizer and a portion of said mixture is continuously returned to said pulverizer, a portion of the mixture discharged from said pulverizer being continuously discharged from said system, means defining an annular grinding zone within the lower portion of the enclosing pulverizer housing, said means including a member having an upwardly facing grinding surface or annular formation about a vertical axis, means forming an annular throat adjacent the inner circumference of said grinding member, means for supplying air to said pulverizer to replace air discharged from said system comprising a pipe arranged coaxially with saidthroat and providing an outlet at its upper end in a zone centrally of and above said throat, means for returning a portion of the fluent mixture to said pulverizer in an upwardly directed annular stream surrounding said pipe, means for causing said air and said returned fluent mixture to become mingled in an annular zone below and adjacent said throat, and means for directing the resulting mixture upwardly through said throat.

3. In an air swept pulverizer adapted for inclusion in a pulverized material circulating system wherein a fluent mixture of material and air is continuously discharged from said pulverizer and a portion of said mixture is continuously returned tq said pulverizer, a portion oi the mixture discharged from said pulverizer being continuously discharged from said system, means defining an annular grinding zone within the lower portion of the enclosing pulverizer housing, said means including a member having an upwardly facing grinding surface of annular tormation about a vertical axis, means forming an annular throat adjacent the inner circumference of said grinding member, means for supplying air.

to said pulverizer to replace air discharged from said system comprising a pipe arranged coaxially with said throat and providing an outlet at its upper end in a zone centrally of and above said throat, means for returning a portion of the fluent mixture to said pulverizer in an upwardly directed ranged coaxially within the lower portion of the pulverizer housing, a circular row of rollable grinding elements positioned intermediate said rings to define an annular pulverizing zone, means for rotating one of said rings and thereby causing said grinding elements to roll relative to both of said rings an inverted cup-like member rotatable about the axis of said rings and extending downwardly into the space inwardly of said rings in defining an annular throat adiacent the inner periphery of said lower ring, means for supplying air to said pulverizer comprising a pipe extending upwardly into said member for delivering said air to'the interior of said member at a level above said throat, means for reversing the direction of flow of said air to cause said air to flow downwardly in an annular stream surrounding said pipe, means for returning aircontaining pulverized material to said pulverizer in an annular stream in opposition to the downward flow of said first named stream of air, said returned material-laden air constituting a portion of the total discharge of air from said pulverizer, a deflector ring surrounding said pipe having 'oppositely inclined conical surfaces converging at a location below said throat for defleeting said annular streams outwardly in inter-' ranged coaxially within the lower portion or the pulverizr housing, a circular row of rollable grinding elements positioned intermediate said rings to define an annular pulverizing zone, means for rotating one of said rings and thereby causing said grinding elements to roll relative to both of said rings, an inverted cup-like member rotatable about the axis of said rings and extending downwardly into the space inwardly of said rings for-defining an annular throat adjacent the inner periphery of aid lower ring, means for supplyi air to sai pulverizer comprising a pipe e tending upwardly into said member-for delivering said air to the interior of said member at a level above said throat, means for reversing the direction of flow of said air to cause said air to flow downwardly in an annular stream surrounding said pipe, means for returning air containing pulverized material to said pulverizer in an annular stream in opposition to the downward flow of said first named stream or air, said returned material-laden air constituting a portion of the total discharge of air irom said pulverizer. a deflector ring surrounding said pipe having oppositely inclined conical surfaces converging at a location below said throat for deflecting said annular streams outwardly in intersecting relation toward an annular zone below and adjacent said throat, thereby causing said separate streams to be mingled in said outer annular zone, and means including an upwardly flaring conical surface for directing the resulting mixture from said mingling zone into said throat, said suri'ace defining the outer boundary of said mingling zone and teminating at the outer periphery of said annular throat.

6. In an air swept pulverizer adaptedv for inclusion in a circulation system such as described, means forming an annular grinding zone within the lower portion of the. enclosing pulverizer housing, means including a downwardly expanding bell-shaped member for defining an annular throat adjacent the inner periphery of said grinding zone, said member terminating in a rounded lower rim portion forming the inner circumferentiai boundary of said throat, means for supplying fluid streams of different densities to said pulverizer for subsequent mingling and flow through said throat, means for admitting one of said prising a pipe arranged centrally of said bellshaped member and extending upwardly therein beyond the level of said lower rim portion and throat, means for admitting the other of said shaped member, a deflector ring contiguous to and surrounding said pipe having an upperand a lower conical surface inclined in opposite directions from adjacent said pipe and converging in an outer peripheral edge spaced from said pipe at a level intermediate said throat and the area of admission of said second named stream, said conical surfaces being so positioned inrelation to the flow of said streams that said streams are defiected outwardly thereby in mixing relation into an annular zone below and closely adjacent said throat, and means for directing the resulting mixture upwardly through said throat.

7. In an air swept pulverizer adapted for inclusion in a circulation system such as described, means forming an annular grinding zone within the lower portion of the enclosing pulverizer housing, said means including a grinding ring having a grinding surface formed annularly about a vertical axis, a downwardly expanding bellshaped member rotatable relative to said ring about said axis and terminating in a lower rim portion inwardly of said grinding ring to form an annular throat, means for supplying fiuid streams of different densities to said pulverizer for subsequent mingling and flow through said throat, means for admitting each of said streams to the interior of said pulverizer in an upward direction, the area of admission for one of said streams being disposed centrally of said bellshaped member at a level above said throat, the area of admission for the other of said streams being arranged annularly of said first named area at a level below said throat, means for directing said streams to a common annular zone below and adjacent said throat, said last named means including surfaces of annular formation arranged to deflect said streams outwardly in intersecting relation into said zone, means including an upwardly flaring conical wall forming the outer boundary of said annular zone for directing the resulting mixture upwardly toward said throat, and a circumferentially spaced series of inclined vanes on said rotatable bell-shaped member for maintaining said throat clear of obstructing material. I

8. In an air swept pulverizer adapted for inclusion in a circulation system such as described, means forming an annular grinding zone within the lower portion of the enclosing pulverizer housing, said means including a grinding ring having a grinding surface formed annularly about a vertical axis, a downwardly expanding bellshaped member rotatable relative to said ring about said axis and terminating in a lower rim portion inwardly of said grinding ring to form an annular throat, means for supplying fluid streams of different densities to said pulverizer for subsequent mingling and flow through said throat, means for admitting each of said streams to the interior of said pulverizer in an upward direc-, tion, the area of admission for one of said streams being disposed centrally of said-bell-shaped memher at a level above said throat, the area of admission for the other of said streams being streams to the interior of said pulverizer comiv arranged annularly of said first named area at a level below said throat, means fordlrecting said streams to a common annular zone below and adjacent said throat, said last named means including'surfaces of annular formation arranged to deflect said streams outwardly in intersecting relation into said'zone, means including an up-- wardly flaring conical wall forming the outer boundary of said annular zone for directing the resulting mixture upwardly toward said throat; a circumferentiallyspaced series of inclined vanes onsaid rotatable bell-shaped member for maintaining said throat clear of obstructing material,

and a plow on said member extending downwardly into said annular mingling zone to the level of said annular deflecting surfaces.

9. In' combination, an air swept pulverizer adapted forincluslon in a circulating system such as describedmeans forming an annular grindin zone within the lower portion of. the pulverizer? housing, means forming an annular throat adja-g, cent a circumference of said grinding zone, means for admitting fluid streams of different densities to said pulverizerfor subsequent mingling and upward flow through said throat, means forming Y openings concentrically arranged with respect to said vertical axis for admitting said streams to said pulverizer at vertically separated locations above and below the' level oi'sa'id throat, the lower of said openings being annular, means for conducting said fluid streams to said-openings comprising a multi-duct' structure having horizoutally disposed conduit portions extending to-- ward said vertical axis from diametrically opposite directions, an upright pipe section forming an elbow extension of. one'of said conduit portions and providing said fluid admission Opening above the level of. said throat. the other of said conduit portions being formed with side walls spaced from said upright pipe section and terminating adjacent the outer circumference of said annular fluid admission opening, said other 0011- dull; portion h vingan annular bottom wall portion surrounding said upright pipe section and extendingupwardly at an inclination to said vertical axis, said annular bottom wall portion terminating in an inclined arcuate lip portion overlying a portion of the horizontally projected area of said annular opening to effect substantially uniform distribution of the entering fluid 7 throughout the available entrance area, means for directing said separately admitted fluid streams to an annular zone below and adjacent said throat, and for causing said streams to be mingled substantially throughout said zone, and means for directing the resulting mixture upwardly from said zone into and through said throat. I

10. In a pulverizer having grinding elements in the lower portion of an enclosing'housing, said housing having an outlet leading from its upper portion, said elements including a member formed with a grinding surface arranged annularly about a vertical axis between a material inlet circumference and a material outlet circumference disposed at different radial spacings from said axis,

' means for feeding material to be pulverized to a region adjacent said inlet circumference, means forming an annular throat adjacent said outlet circumference, means for causing carrier fluid to flow through said throat for transporting particles of pulverizedmaterial to and through said outlet, means for admitting said carrier fluid to said pulverizer in separate upwardly directed concentric streams of which an inner stream is of lower density than an outer stream. said inner stream being admitted to the interior of said REFERENCES CITED housing t level higher t h level of The following references are-o1 record in the mission 01' said outer stream, means defining an file this P t! annular space in the region below and adjacent 5 TENTS .said throat, means for causing said streams to FOREIGN PA become mingled in said annular space to form a. Date mixture thereof. and means 101- directing said 154,112 m A 8, 04 mixture upwardly through said throat.

' RALPH M. HARDGROVE. X0 

